Simple calculator done for The Complete Ruby on Rails Developer Course

simple_calculator.rb

module CalculatorStrategy
  def calculate(number_a, number_b)
    raise "Not implemented"
  end
end

class AdditionStrategy
  include CalculatorStrategy

  def calculate(number_a, number_b)
    number_a + number_b
  end
end

class MultiplicationStrategy
  include CalculatorStrategy

  def calculate(number_a, number_b)
    number_a * number_a
  end
end

class DivisionStrategy
  include CalculatorStrategy

  def calculate(number_a, number_b)
    number_a / number_b
  end
end

class SubtractionStrategy
  include CalculatorStrategy

  def calculate(number_a, number_b)
    number_a - number_b
  end
end

class Calculator
  def set_strategy(new_strategy)
    @strategy = new_strategy
  end

  def calculate(number_a, number_b)
    @strategy.calculate(number_a.to_i, number_b.to_i)
  end
end

class CalculatorPresenter
  def initialize(engine)
    @engine = engine
  end

  def get_strategy
    strategies = {
      1 => MultiplicationStrategy,
      2 => AdditionStrategy,
      3 => SubtractionStrategy,
      4 => DivisionStrategy,
    }
    strategies[@operation].new
  end

  def calculate_result
    @engine.set_strategy(get_strategy)
    @engine.calculate(@first_number, @second_number)
  end

  def present
    puts "Simple calculator"
    20.times { print "-" }
    puts
    puts "Enter the first number"
    @first_number = gets.chomp.to_i
    puts "Enter the second number"
    @second_number = gets.chomp.to_i

    puts "Select the operation you'd want to make:"
    puts "\t1. Multiplication"
    puts "\t2. Addition"
    puts "\t3. Subtraction"
    puts "\t4. Division"
    @operation = gets.chomp.to_i

    20.times { print "-" }
    puts
    puts "Result is: #{calculate_result}"
  end
end

calculator = CalculatorPresenter.new(Calculator.new)
calculator.present